METHOD FOR THE BIOLOGICAL PURIFICATION OF NITRATE-CONTAINING WATER

Description

[0001] The present invention relates to the technical field of biological reduction of the nitrate nitrogen concentration in nitrate-containing water, in particular raw water and / or wastewater, based on lithotrophic nitrate elimination.

[0002] In In this context, the present invention relates to a process for the biological purification of raw water, in particular for the biological reduction of the nitrate nitrogen concentration in nitrate-containing raw water (Nitrogen Elimination System: "NELIS"), with microbial lithotrophic nitrate elimination using and / or colonization of biomass.

[0003] Nitrates are water-soluble salts of nitric acid, which are formed as part of the nitrogen cycle through the metabolic conversion of nitrogen-containing compounds by nitrifying bacteria in the soil. The nitrates, in turn, are absorbed by plants and used as a nitrogen source by plant metabolism or converted into atmospheric nitrogen by so-called denitrifying (soil) bacteria.

[0004] However, human influences, particularly the agricultural use of nitrogen-containing fertilizers, manure, and pesticides, disrupt the natural nitrogen cycle, leading to excessive nitrate accumulation in the soil. Due to its high water solubility, nitrate is leached from the soil and enters the groundwater. As a result, groundwater, surface water, and well water often exhibit elevated nitrate concentrations. Furthermore, excess nitrate in groundwater can also lead to elevated nitrate concentrations in rivers, lakes, and oceans.

[0005] Furthermore, wastewater can also be heavily contaminated with nitrates. This applies to both industrial and municipal wastewater, with urea from feces and protein compounds being the most common sources of nitrates. Given the previously described, sometimes severe nitrate contamination of groundwater, surface water, and well water (so-called raw water), wastewater generated during the treatment of raw water can also be contaminated with nitrates.

[0006] Elevated nitrate levels in groundwater, surface water, and well water, as well as in water bodies and nitrate-contaminated wastewater, are problematic in many ways. Particularly problematic is that the infiltration of nitrate into groundwater increasingly endangers drinking water quality. Even though nitrates and nitrate anions are not toxic to humans and animals, they can be converted into toxic nitrite and carcinogenic nitrosamines in the body. The "Regulation on the Quality of Water for Human Consumption" (Drinking Water Regulations - TrinkwV) therefore sets a maximum limit of 50 mg / l for the nitrate concentration in drinking water.

[0007] Various chemical-physical processes for removing nitrate from raw water and wastewater are known in the state of the art, such as ion exchangers, reverse osmosis, or nanofiltration. However, the chemical-physical processes known in the state of the art are partly environmentally harmful and, moreover, often costly and resource-intensive, requiring extensive equipment. Furthermore, these processes, such as nitrate removal with ion exchangers, do not necessarily lead to a reduction of nitrate to elemental nitrogen, but merely to the binding of the nitrate, so further, particularly chemical, post-treatment is necessary for final nitrate elimination.

[0008] Furthermore, it is possible to reduce the nitrogen content in raw water and wastewater through biological processes, particularly those using microorganisms. Biological processes are significantly more environmentally friendly and resource-efficient than chemical-physical processes. Furthermore, the conversion of nitrate into elemental or atmospheric nitrogen is possible. However, the biological processes known to date are only used with significant or increased use of auxiliary materials. In addition, biological processes can have an unfavorable CO2 footprint.

[0009] However, heterotrophic processes, particularly heterotrophic denitrification, for nitrogen or nitrate elimination have some disadvantages: The process economics can be unfavorable, as external carbon sources may have to be added as electron donors. Furthermore, the rapid growth of heterotrophic bacteria often leads to significant excess sludge production, which in turn has a negative impact on the process economics. In addition, biological heterotrophic processes for nitrate degradation in nitrate-contaminated water are only economically viable for waters with a high COD (chemical oxygen demand) or high BOD (biochemical oxygen demand). If the COD or BOD is too low or has low microbial availability, additional external carbon sources must be used. This is particularly true for nitrate-contaminated raw waters, such asWell or groundwater, or wastewater without significant amounts of organic substances usually have only a low COD or BOD and cannot be treated with the known biological processes for nitrate elimination or only with the use of additional carbon sources.

[0010] Overall, both the chemical-physical processes known in the state of the art for nitrate elimination from nitrate-containing water, in particular raw and / or waste water, as well as the heterotrophic biological nitrate elimination processes are associated with disadvantages and are in need of improvement in several respects.

[0011] The document JP 2003 154393 A discloses a known process for the elimination of nitrates from wastewater.

[0012] Taking into account the above statements regarding the disadvantages of the prior art, the present invention is based on the Task The aim of the invention is to provide a process for removing nitrates from nitrate-containing water, particularly raw water and / or wastewater, which overcomes or at least mitigates the aforementioned disadvantages. In particular, the present invention aims to provide a process that exhibits a good nitrate nitrogen removal rate and is resource-saving, environmentally friendly, and universally applicable to various waters, while also avoiding the problem of excess sludge production.

[0013] To Solution To achieve the above-described object, the present invention proposes a process for the biological purification of water, in particular for the biological reduction of the nitrate nitrogen concentration in nitrate-containing water, with microbial nitrate elimination according to claim 1.

[0014] Within the scope of the present invention, it has surprisingly been possible to overcome the disadvantages described in the prior art by means of a lithotrophic biological nitrate elimination process, which is based in particular on a specially selected biomass. In this context, it was particularly surprising that the consortium of microorganisms used is capable of degrading nitrate in nitrate-containing water under lithotrophic cultivation or environmental conditions.

[0015] The process according to the invention is associated with numerous advantages and special features, which are described below: Given that the process according to the invention is a biological process for water purification, in particular for the purpose of nitrate elimination, the process is overall resource-saving and requires little energy, since the conversion of nitrate into elemental nitrogen is catalyzed by microorganism-based biomass. Overall, the process according to the invention thus provides an environmentally friendly, resource-saving, and cost-effective way to reduce the nitrate nitrogen concentration in water.

[0016] Furthermore, the process according to the invention is versatile, i.e., suitable for various nitrate-containing waters. Within the scope of the present invention, the process according to the invention can be used to significantly reduce the nitrate nitrogen content in both raw water, such as groundwater, well water, or spring water, as well as in wastewater. In particular, the process according to the invention can also be used as a preliminary stage for drinking water treatment in order to achieve a nitrate content in the water of less than 50 mg / l, i.e., a nitrate content below the maximum permissible nitrate content for drinking water.

[0017] In addition, it was surprisingly found within the scope of the present invention that the rapid growth of heterotrophic microorganisms and the associated excess sludge production can be suppressed if the biological nitrogen elimination is carried out as lithotrophic nitrate elimination. In this context, it has proven advantageous to keep the concentration of organic carbon compounds contained in the water to be treated, measured by the biochemical oxygen demand BOD 5 and the chemical oxygen demand COD, i.e. the amount of all organic substances present in the water that are oxidizable under certain conditions, low or to assume that it is concentrated at a low level. According to the invention, it can be provided in particular that the water to be treated contains inorganic oxidizable substances, but that the concentration of organic oxidizable substances is kept low or is assumed to be concentrated at a low level.

[0018] Against this background, the biological process according to the invention is particularly suitable for the nitrate elimination from raw water and / or wastewater which has a low BOD 5 or COD, such as well water or groundwater or in particular industrial wastewater which is free from fecal or other organic contaminants. The biological treatment of water with a low COD or low BOD 5 has so far made little sense from a process economics point of view, since the addition of carbon sources, e.g. in the form of methanol, was necessary for the known heterotrophic nitrate elimination processes. Within the scope of the present invention, it was found, completely surprisingly, that the process according to the invention enables the biological treatment of this water even without the addition of external carbon sources.

[0019] Furthermore, the process according to the invention is characterized by its good nitrate degradation performance. With the process according to the invention, the nitrate concentration can be reduced even in heavily nitrate-contaminated waters to values ​​below the maximum limit of 50 mg / l nitrate specified for drinking water in the "Ordinance on the Quality of Water for Human Consumption" (Drinking Water Ordinance). In other words, the process according to the invention even makes it possible to treat nitrate-containing waters to achieve drinking water quality.

[0020] Furthermore, it has been shown within the scope of the present invention that the nitrate degradation rates achieved with the process according to the invention as well as the total nitrogen degradation rates can be further improved by a targeted adjustment of the process parameters, in particular on the basis of the targeted adjustment of the residence time of the nitrate-containing water in the biomass or sludge bed, the dissolved oxygen concentration and the pH value as well as the bed load, ie the amount of nitrate with which a defined volume of the biomass is loaded per day.

[0021] With regard to the advantages and special features of the process according to the invention, in particular the nitrate degradation rates achieved with the process, reference is made at this point to the exemplary embodiments described in more detail below, which further demonstrate the advantages and effectiveness of the process according to the invention. These advantages and special features are to be considered as evidence of the existence of an inventive step.

[0022] For a better understanding of the present invention, the most important terms relating to the process according to the invention are explained below: Regarding the term "biomass," this is used in connection with the process according to the invention to refer to a cell mass based on microorganisms. The microorganisms are predominantly bacteria and archaea. However, under certain circumstances, fungi, algae, or other microorganisms may also be present in the biomass. Within the scope of the process according to the invention, the biomass forms a sludge or biomass bed in the reaction chamber, which is in contact with the nitrate-containing water, in particular, around which the latter flows. According to a particularly preferred embodiment, a biomass or sludge bed based on biomass in the form of pellets and / or granules is used for the process according to the invention.For further information regarding biomass in the form of pellets and / or granules, please refer to the following explanations and the examples of implementation described further below.

[0023] In the context of the present invention, the term "nitrate elimination" refers to the preferably microbial conversion of nitrogen bound in the form of nitrate to molecular nitrogen or nitrogen gas and nitrogen oxides under lithotrophic conditions, i.e., using inorganic compounds or substances for energy production, by a consortium of various microorganisms. The microorganisms used for nitrate elimination are involved in the sulfur, methane, nitrogen, and iron cycles. Molecular nitrogen can arise as a direct metabolic product from the microbial metabolism of nitrate or as an indirect reaction product through the chemical conversion of nitrate with microbial metabolic products, without wishing to be limited to this theory.

[0024] "Nitrogen cycle" in the context of the process according to the invention refers to the cycle of the element nitrogen in the biosphere. The steps of the nitrogen cycle are nitrogen fixation (conversion of chemically inert N2 into bioavailable ammonium, preferably by microorganisms), nitrification (microbial conversion of ammonia to nitrate), nitrogen assimilation (formation of organic nitrogen compounds from inorganic nitrogen compounds), ammonification (conversion of organic nitrogen compounds to ammonia or ammonium), nitrate reduction (reduction of nitrate to nitrite), denitrification (reduction of nitrate and nitrite to molecular nitrogen), and To aerobic Amm onium Ox idation or the so-called anammox process (reaction of ammonium and nitrite to molecular nitrogen).

[0025] Denitrification plays a particularly important role in the process according to the invention—without wishing to limit itself to this theory. Denitrification is catalyzed by various microorganisms, which are referred to as denitrifiers. The microorganisms involved in the nitrogen cycle used in the process according to the invention or contained in the biomass are preferably established under anaerobic and lithotrophic environmental conditions or are viable under anaerobic and lithotrophic environmental conditions.

[0026] The term "lithotrophic" is to be understood in the context of the present invention to mean that the microorganisms used according to the invention use inorganic reducing agents or electron donors for their anabolism and / or biosynthesis, in particular for energy production.

[0027] Furthermore, the biomass used for the process according to the invention or the biocenosis formed and / or settled in the reaction chamber contains microorganisms, in particular bacteria and / or archaea, which are involved in the sulfur cycle, i.e. the system of chemical transformations of sulfur and sulfur-containing compounds. The microorganisms involved in the sulfur cycle can, for example, belong to the sulfur-reducing or sulfur-oxidizing bacteria and the genera Syntrophobacter, Thiobacillus, Desulfovibrio and / or Sulfuritalea Within the scope of the present invention, it may be provided in this context, in particular, to adjust the environmental conditions in such a way that microorganisms involved in the sulfur cycle can settle in the reaction space, in particular the nitrate-containing water, and can carry out anaerobic, lithotrophic metabolism.

[0028] In the context of the present invention, microorganisms involved in the iron cycle are understood to mean, on the one hand, iron-oxidizing microorganisms, also synonymously referred to as iron bacteria, which obtain energy by oxidizing divalent iron (Fe(II)) and operate an anaerobic or facultative anaerobic metabolism. Iron-oxidizing microorganisms can, for example, belong to the genera Thiobacillus and / or Acidovorax Likewise, within the scope of the present invention, the microorganisms involved in the iron cycle are also understood to include iron-reducing bacteria that reduce trivalent iron (Fe(III)) to divalent iron (Fe(II)). Iron-reducing microorganisms can, for example, belong to the genera Geobacter, Thauera and / or Rhodoferax belong to.

[0029] Furthermore, the biomass used for the process according to the invention contains microorganisms, in particular bacteria and / or archaea, which are involved in the methane cycle. The microorganisms involved in the methane cycle include, among others, methanogens, in whose energy metabolism methane is formed (also referred to as methanogenesis). Methaneogens can in particular belong to the genera Methanosaeta, Methanobacterium, Methanoregula, Methanosarcina, Methanosphaerula and / or Methanospirillum belong to.

[0030] According to a particularly preferred embodiment, the biomass used in the process according to the invention comprises microorganisms of the genera Methanosaeta, Methanobacterium, Syntrophobacter, Acidovorax, Methanoregula, Anaerolinea, Thiobacillus, Methanosarcina, Geobacter, Methanoculleus, Desulfovibrio, Sulfuritalea, Thauera, Methanosphaerula, Azoarcus, Methanothermobacter, Pseudomonas, Stenotrophomonas, Lysobacter, Pseudoxanthomonas, Methanospirillum and / or Rhodoferax, The above list is not to be understood as exhaustive.

[0031] It is envisaged that activated sludge cultivated, i.e. grown, under anaerobic and heterotrophic conditions is used as the biomass for the process according to the invention. Activated sludge cultivated or grown under anaerobic conditions usually contains a diverse consortium of microorganisms, including microorganisms involved in the nitrogen, sulfur, methane, and iron cycles. Biomass or suitable activated sludge suitable for the present invention is obtained from a heterotrophic, anaerobic activated sludge process for the treatment of wastewater with a high COD content or COD pollution. In this context, it was completely surprising that activated sludge originally cultivated or grown heterotrophically is suitable for the biological nitrate elimination from raw water and wastewater under lithotrophic environmental conditions.the microbial metabolic processes of the microorganisms involved in the nitrogen, iron, sulphur and methane cycles taking place under lithotrophic conditions lead to nitrate degradation in nitrate-containing water, in particular raw water and / or wastewater.

[0032] In order to establish environmental conditions that enable lithotrophic nitrate elimination by microorganisms involved in the nitrogen, methane, iron, and sulfur cycles, it is provided that the process and / or the nitrate elimination is carried out under anoxic conditions. Likewise, it is preferred if the nitrate-containing water is adjusted to low-oxygen, in particular anoxic, conditions during the process and / or the nitrate elimination. It is particularly advantageous with regard to the present invention if the process and / or the nitrate elimination is carried out at a dissolved oxygen concentration of at most 3 mg / l, in particular at most 2 mg / l, preferably at most 1 mg / l, based on the water.

[0033] In order to improve the process efficiency - both with regard to avoiding the production of excess sludge by colonizing heterotrophic microorganisms or converting the metabolism of the microorganisms to heterotrophic conditions and also with regard to reducing costs - it is also preferred if the process according to the invention and / or the nitrate elimination is carried out without the addition of organic carbon sources.

[0034] As already stated above, the process according to the invention is suitable for nitrate removal or reduction of the nitrate content in various types of water. According to a preferred embodiment of the process according to the invention, raw water and / or wastewater, in particular raw water, can be used as the nitrate-containing water.

[0035] For the purposes of the present invention, the term "raw water" refers to any untreated water that originates from surface sources, such as ponds, dams, lakes or rivers, or from subsurface water sources, such as wells or groundwater.

[0036] For the purposes of the present invention, the term "wastewater" refers to water or wastewater whose properties have been altered by domestic, commercial, agricultural, or other use, as well as water or rainwater flowing from precipitation from built-up or paved areas and collected for further transport, as well as other water flowing together with wastewater or rainwater into wastewater treatment plants. With regard to nitrate elimination from wastewater, the process according to the invention is particularly suitable for the purification of wastewater that is only slightly contaminated with organic substances or wastewater that has been at least substantially freed of organic components prior to implementation of the process according to the invention.The process according to the invention is particularly suitable, for example, for removing nitrate from wastewater which has accrued during the treatment of raw water into drinking water.

[0037] With regard to the properties of the nitrate-containing water, it is preferred according to the invention if the nitrate-containing water has a relatively low chemical oxygen demand (COD) at the time of feeding into the reactor. Within the context of the present invention, the chemical oxygen demand or COD is understood to be a measure of the sum of all oxidizable substances present in the nitrate-containing water. The COD thus indicates the amount of oxygen (unit: mg / l) that would be required to oxidize the oxidizable substances present in the nitrate-containing water if oxygen were the oxidizing agent. The chemical oxygen demand serves in particular as a sum parameter for quantifying the contamination of wastewater with organic substances and includes both biodegradable and non-biodegradable organic substances as well as inorganic substances.The chemical oxygen demand can be determined, for example, by a photometric measuring method according to DIN 15705 or a volumetric analytical measuring method according to DIN 38409-H41.

[0038] According to the invention, the nitrate-containing water has a chemical oxygen demand COD [mg O 2 / l] in the range of 0 to 50 mg / l, preferably 0 to 25 mg / l, particularly preferably 0 to 10 mg / l, based on the nitrate-containing water at the time of feeding into the reaction chamber.

[0039] The use of nitrate-containing water with a low COD or a COD concentration within the aforementioned ranges prevents the microorganisms from converting to heterotrophic growth or heterotrophic metabolism, and prevents the colonization of heterotrophically growing microorganisms in the reaction chamber. In other words, the use of nitrate-containing water with a COD within the aforementioned range ensures that process or environmental conditions for lithotrophic nitrate elimination are created and maintained. In this context, it can also be provided that a treatment stage for adjusting, in particular lowering or reducing, the COD in the nitrate-containing water precedes the process according to the invention.

[0040] Furthermore, regarding the raw water to be treated for the process according to the invention, it can be provided that it has a defined biochemical oxygen demand (BOD). The biochemical oxygen demand is the measure of the amount of oxygen dissolved in the water, which is required for the microbial or biological degradation of dissolved organic compounds in the wastewater. In this context, the BOD 5 indicates the amount of oxygen (in mg / l) that the microorganisms in a water sample would consume over a period of five days at a temperature of 20 °C to aerobically degrade the constituents contained in the water.

[0041] In other words, the biochemical oxygen demand is an indirect measure of the total amount of all biodegradable organic substances in the water. The biochemical oxygen demand indicates how much dissolved oxygen is required for the biological degradation of the organic wastewater constituents or raw water constituents in a given period of time. BOD 5 can be determined using manometric or respiratory methods. It can also be determined using the dilution method according to DIN EN 1899-1.

[0042] Particularly good results or nitrate degradation performance are achieved according to the invention when the nitrate-containing water has a biological oxygen demand (BOD 5) in the range of 0 to 75 mg / l, in particular at most 50 mg / l, preferably at most 40 mg / l, preferably at most 30 mg / l, particularly preferably at most 20 mg / l, based on the nitrate-containing water at the time of introduction into the reaction chamber. In other words, it is preferred according to the invention if the BOD 5 of the nitrate-containing water is as low as possible.

[0043] The nitrate concentration in the nitrate-containing water at the time of introduction into the reaction chamber can vary widely. According to the invention, the nitrate-containing water has a nitrate concentration in the range of 5 to 500 mg / l, preferably 8 to 250 mg / l, most preferably 10 to 100 mg / l, based on the nitrate-containing water at the time of introduction into the reaction chamber. As will be further demonstrated by the exemplary embodiments described below, the process according to the invention is characterized by an excellent nitrate degradation performance and nitrate degradation rate.

[0044] In this context, it can be provided within the scope of the method according to the invention that the nitrate concentration of the nitrate-containing water in the inlet to the reaction chamber is measured.

[0045] The process according to the invention achieves a significant reduction in the nitrate content or nitrate concentration in the treated nitrate-containing water. According to the invention, it can be provided, in particular, that the nitrate-containing water, at the time of leaving the reaction chamber, has a nitrate concentration in the range of 0.01 mg / l, in particular 0.1 mg / l, preferably 1 mg / l, preferably 2 to 200 mg / l, preferably 3 to 100 mg / l, even more preferably 4 to 50 mg / l, further preferably 5 to 10 mg / l, based on the nitrate-containing water at the time of leaving the reaction chamber.

[0046] As can be seen from the exemplary embodiments described in detail below, nitrate degradation rates and / or total nitrogen degradation rates of approximately 90%, based on the nitrate or total nitrogen content of the nitrate-containing water at the time of feeding into the reaction chamber, can be achieved with the process according to the invention.

[0047] In addition, it can also be provided according to the invention to adapt further parameters, such as the temperature, the composition of the nitrate-containing water, the residence time of the nitrate-containing water in the reactor, the pH value and the subsequently specified boundary layer renewal of the biomass, within the scope of the method according to the invention, and thus also to adapt the adapted biomass or biocenosis or to adjust it to the aforementioned parameters.

[0048] With regard to the biomass used in the process according to the invention, a particularly preferred embodiment provides for the biomass to form a biofilm on a carrier material. In particular, the carrier material may form a type of matrix or framework on which the biomass, in particular the microorganisms, grow sessile. The growth of the biomass on the carrier material is associated with advantages. Firstly, biofilm formation on a carrier material allows for easier separation of the biomass from the nitrate-containing water. Secondly, growth on the carrier material creates favorable environmental and growth conditions for the microorganisms involved in nitrate elimination.

[0049] With regard to the carrier material in particular, according to a preferred embodiment of the present invention, the carrier material can contain (i) inorganic and / or organic, preferably inorganic salts, in particular carbonates, particularly preferably calcium carbonate (lime); (ii) metals and / or transition metals, in particular iron; and / or (iii) non-metals, in particular sulfur and / or nitrogen. In the carrier material based on the aforementioned substances, the calcium carbonate or lime forms a type of framework or matrix on which the biomass grows. The carrier material is formed by the microorganisms involved in nitrate elimination themselves, in particular when they are cultivated under anaerobic, reducing conditions.

[0050] Furthermore, it is preferred if the carrier material contains metals or transition metals, in particular iron, as well as non-metals, in particular sulfur and / or nitrogen. The remaining ingredients, in particular iron, sulfur, and nitrogen, contribute—without wishing to be limited to this theory—to the reducing reaction conditions in the nitrate-containing water and thus support nitrate elimination. In particular, the metals, transition metals, and non-metals can be used by the microorganisms contained in the biomass as electron acceptors and / or electron donors and thus serve to generate energy or maintain microbial lithotrophic metabolism. By establishing and maintaining reducing conditions in the nitrate-containing water, the overall maintenance of the biocenosis and thus also the reduction of nitrate to elemental nitrogen is further promoted.

[0051] According to a particularly preferred embodiment of the process according to the invention, it can also be provided that biomass is used in the form of granules and / or pellets (granulated sludge or pellet sludge). As explained in more detail below, biomass in the form of granules or pellets can be particularly efficiently dispersed or fluidized in the nitrate-containing water, thus supporting and maintaining the constant mass transfer between the nitrate-containing water and the biomass. The improvement in mass transfer, in turn, benefits the nitrate or total nitrogen degradation rate.

[0052] The granules or pellets are preferably aggregations of the biomass used, which are stabilized by calcium carbonate frameworks as a carrier material, i.e. the carrier material described above, and also contain metals or transition metals and non-metals, preferably iron, sulfur and / or nitrogen.

[0053] With regard to the granules or pellets, the invention can further provide for them to have an average particle size, in particular an average particle diameter, in the range from 0.01 to 150 mm, in particular 0.05 to 100 mm, preferably 0.1 to 50 mm, more preferably 1 to 25 mm, particularly preferably 2 to 20 mm, further preferably 3 to 15 mm, and even more preferably 5 to 10 mm. The particle size of the granules or pellets can be determined using methods generally known to those skilled in the art, in particular by light microscopy. The aforementioned particle sizes have the advantage that, on the one hand, good fluidization of the biomass in the reaction chamber or nitrate-containing water is possible, and, on the other hand, the biomass remains readily accessible to the nitrate-containing water due to the volume / surface ratio.

[0054] Pellets or granules with a lime-, iron-, nitrogen-, and sulfur-containing carrier material, which are suitable for the process according to the invention, can be obtained, for example, from a biological treatment stage for highly contaminated COD-containing wastewater. The biofilm on the carrier materials comprises a consortium of microorganisms involved in the nitrogen, methane, iron, and sulfur cycles. For further information regarding the extraction or provision of a suitable biomass for the process according to the invention, reference can also be made to the exemplary embodiments described in more detail below.

[0055] Within the scope of the present invention, it has also proven advantageous if the biomass, preferably biomass in the form of granules and / or pellets, is fluidized and / or dispersed in the nitrate-containing water. Fluidization or dispersion of the biomass in the nitrate-containing water ensures the exchange of substances between the biomass and the nitrate-containing water. This prevents, in particular, the biomass from settling or compacting at the bottom of the reaction chamber, thus becoming inaccessible to the metabolic processes or chemical reactions required for nitrate reduction.

[0056] The nitrate degradation rates or performance of the process according to the invention can also be further improved if the process and / or the nitrate elimination is carried out with a bed loading [amount of nitrogen per volume of biomass per unit time] in the range of 0.5 to 1,000 gN / m 3 / d, in particular 1 to 500 gN / m 3 / d, preferably 5 to 250 gN / m 3 / d, more preferably 10 to 100 gN / m 3 / d, particularly preferably 30 to 65 gN / m 3 / d. As explained in the following exemplary embodiments, the nitrate degradation rate can be significantly influenced, in particular promoted, by a targeted adjustment of the bed loading.

[0057] In the context of the present invention, bed loading refers to the total amount of nitrogen (unit: g) with which a defined volume of biomass (unit: m 3 ) in the reaction chamber, i.e., the "biomass bed" or "sludge bed" in the reaction chamber, is loaded per unit of time (unit: d or day) in the process according to the invention. Taking the bed loading into account or incorporating it, the process according to the invention can be applied to all types of reaction chambers, since the amount of nitrogen introduced into the reaction chamber per unit of time relates to the volume of biomass, regardless of the type, size, or volume of the reaction chamber.

[0058] The process according to the invention can also be carried out in various types of reaction spaces. In principle, all bioreactors, fermentation systems, and reaction tanks for biological water treatment are suitable for carrying out the process according to the invention. According to a first preferred embodiment of the invention, it can thus be provided that the nitrate-containing water is passed through a reactor, in particular a stirred tank reactor, fixed bed reactor, fluidized bed reactor, tubular reactor, and / or membrane bioreactor, preferably a stirred tank reactor. Furthermore, it can also be provided that the nitrate-containing water is passed through a preferably closed reaction tank. This can in particular be a clarification tank, which allows the establishment of anoxic reaction conditions.In other words, according to the invention, it can thus be provided that the reaction space is selected from reactors, in particular stirred tank reactors, fixed bed reactors, fluidized bed reactors, tubular reactors and / or membrane bioreactors, preferably stirred tank reactors, and / or preferably closed reaction tanks.

[0059] To ensure a consistent and efficient nitrate removal rate, or rather, a consistent nitrate and total nitrogen removal rate, the process and / or nitrate removal is carried out with continuous boundary layer renewal at the surface of the biomass. Boundary layer renewal ensures and maintains the mass exchange between the nitrate-containing water and the biomass.

[0060] According to a particularly preferred embodiment of the present invention, the boundary layer renewal is achieved by generating a flow in the nitrate-containing water and / or biomass. In particular, in this context, it can be provided that a flow of the nitrate-containing water and / or biomass is generated in the nitrate-containing water, directed from the lower to the upper end of the reaction chamber.

[0061] For the process according to the invention, all technical means known to the person skilled in the art for adjusting and / or generating boundary layer renewal or for moving the biomass can be used and can be selected and adapted depending on the reaction space or reaction vessel. Suitable technical means for boundary layer renewal and / or for moving the biomass and generating the flow include, for example, stirring devices or stirring shafts, pumps, or circulation devices. The introduction of atmospheric oxygen must be strictly avoided.

[0062] According to a particularly preferred embodiment, the boundary layer renewal in the process according to the invention takes place by stirring. In this context, it is particularly preferred if stirring speeds in the range of 0.1 to 50 revolutions per minute, in particular 0.5 to 25 revolutions per minute, preferably 0.7 to 20 revolutions per minute, more preferably 1 to 10 revolutions per minute, particularly preferably 1.2 to 5 revolutions per minute, even more preferably 1.5 to 2 revolutions per minute are used. Based on the aforementioned stirring speeds, on the one hand, the boundary layer renewal and movement of the biomass can be ensured. On the other hand, however, at the same time, the biomass, preferably in the form of granules or pellets, is prevented from being destabilized by excessive stirring or from disintegrating as a result of the introduction of excessive shear forces.

[0063] Furthermore, it has been shown within the scope of the present invention that the pH has a significant influence on the nitrate degradation rate or total nitrogen degradation rate. According to the invention, the process and / or the nitrate elimination is carried out at a pH in the range of 6 to 8, preferably 7 to 7.5. A pH in the aforementioned ranges improves the environmental conditions in the nitrate-containing water for the biomass used, in particular the microorganisms used.

[0064] Furthermore, the nitrate degradation rate or total nitrogen degradation rate is also influenced by the residence time of the nitrate-containing water in the reaction chamber, especially the biomass-based reaction bed. InIn this context, it has proven particularly advantageous if the process according to the invention and / or the nitrate elimination is carried out with residence times of the nitrate-containing water in the reaction chamber in the range of 0.5 to 100 hours, in particular 1 to 80 hours, preferably 2 to 50 hours, more preferably 5 to 25 hours, particularly preferably 8 to 22 hours. In this context, reference can also be made to the exemplary embodiments described below, which show that with residence times of the nitrate-containing water in the aforementioned ranges, nitrate removal rates of up to 80%, based on the nitrate content of the nitrate-containing water before it is fed into the reaction chamber, can be achieved.

[0065] With regard to the process procedure, it can also be provided within the scope of the present invention that the process according to the invention is carried out continuously and / or discontinuously, preferably continuously. Continuous process procedure is particularly advantageous with regard to process economy. Furthermore, the process is carried out in a single stage.

[0066] In addition, it can be provided according to the invention that the process is followed by a post-clarification and / or precipitation and / or flocculation, in particular wherein the post-clarification and / or precipitation and / or flocculation is carried out in the same or a separate reaction chamber, preferably a separate reaction chamber.

[0067] As a result, the present invention provides an efficient biological process for nitrate elimination from water, in particular raw water and / or wastewater, which overcomes or at least mitigates the disadvantages associated with prior art processes. Overall, the process according to the invention is characterized by good nitrate and total nitrogen removal rates, is environmentally friendly, conserves resources, and is also cost-effective to implement. Furthermore, the problem of excess sludge production, which frequently occurs with prior art biological processes, is avoided.

[0068] Further details and advantages of the subject matter of the invention will become apparent from the following description and the accompanying drawings, in which preferred embodiments of the process according to the invention are illustrated by means of a schematic representation of a reactor plant suitable for the process according to the invention. Fig. 1A is a schematic representation of a reactor plant suitable for carrying out the process according to the invention, and Fig. 1B is a schematic representation of the interior view of a reactor tank during the implementation of the process according to the invention, including an enlarged detail which schematically represents the flow generated in the nitrate-containing water or in the biomass to ensure boundary layer renewal.

[0069] Fig. 1Ashows a schematic representation of a reactor system 1 which can be used to carry out the process according to the invention. The process can be carried out both discontinuously as a batch operation and continuously, preferably continuously. The reactor system 1 comprises a reactor tank 2 with a stirrer shaft 3 and a motor / drive 10 for the stirrer shaft 3. According to a preferred embodiment of the process according to the invention, the reactor tank 2 is a stirred tank reactor or Continuously Stirred Tank Reactor(CSTR) is used. The reactor tank 2 is charged with biomass 11, preferably biomass in the form of granules and / or pellets. The biomass 11 forms a biomass or sludge bed in the reactor tank 2. For nitrate elimination from nitrate-containing water, in particular raw water and / or wastewater, the nitrate-containing water 12 is fed to the reaction chamber, in particular the reactor tank 2, via an inlet 4. Optionally, the reactor system 1 used for the process according to the invention can have an inlet vessel or a reservoir 7 for the nitrate-containing water 12, from which the nitrate-containing water is fed to the reaction chamber, in particular the reactor tank 2, via the inlet 4. Furthermore, according to a preferred embodiment of the process according to the invention, it is preferred if a defined residence time is set for the nitrate-containing water 12 in the reactor tank 2 or biomass bed.Likewise, it is preferred if the nitrate-containing water 12 is fed to the reactor tank 2 or the biomass 11 with a specifically adjusted bed loading. To adjust the bed loading, it can be provided that the total nitrogen and / or nitrate concentration in the nitrate-containing water 12 is measured before being fed into the reactor tank 2, preferably in the inlet 4 and / or in the feed vessel or in the receiver 7. With regard to the process according to the invention, it can also be provided that the biomass 11 is fluidized with the nitrate-containing water 12 and agitated for the purpose of boundary layer renewal. This is preferably done by stirring with the stirrer shaft 3. After the residence time of the nitrate-containing water in the biomass bed or the sludge bed has elapsed, the nitrate-containing water 12 leaves the reactor tank 2 via the outlet 5. The inflow and outflow of the nitrate-containing water before and after the end of the residence time in the biomass or sludge bed.Sludge bed can be controlled via corresponding pumps 15 and (shut-off) valves 8.

[0070] Furthermore, it is possible to monitor and adjust the process parameters using measuring devices 9. In particular, the pH value of the nitrate-containing water 12, the temperature, the dissolved oxygen concentration, the total nitrogen concentration, and the nitrate and / or ammonium concentration can be measured using the measuring devices 9. If necessary, depending on the measured values, nitrate can be added to stimulate and / or accelerate nitrate degradation. Adjustments to the pH value can also be made.

[0071] Fig. 1Balso shows a schematic representation of the interior view of a reactor tank 2 based on a stirred tank reactor in operation during the process according to the invention. The biomass 11 forms a biomass or sludge bed in the reactor tank 2 and is fluidized and / or perfused by the nitrate-containing water 12. In order to ensure boundary layer renewal between biomass 11 and nitrate-containing water 12 to improve the nitrate degradation rate, it is provided - as previously stated - that the process according to the invention is carried out with stirring. The rotation 13 of the agitator shaft 3 is in Fig. 1B indicated. By stirring, a flow 14 can be generated in the nitrate-containing water 12 or the biomass 11, wherein the flow is preferably directed from the lower end of the reactor toward the upper end.

[0072] The Fig. 1A and 1BThe described process according to the invention using the reactor system shown serves to provide a clear explanation and illustration of the process according to the invention and is not intended to be limiting in any way. Other types of reactors, such as fixed-bed reactors, fluidized-bed reactors, tubular reactors or membrane bioreactors, or preferably closed reaction tanks, are equally suitable for carrying out the process according to the invention.

[0073] Preferred embodiments of the present invention are also described below on the basis of the exemplary embodiments, which, however, are also in no way to be understood as limiting. EXAMPLES OF IMPLEMENTATION:

[0074] Based on the exemplary embodiments described below, the efficiency of the process according to the invention was investigated, particularly with regard to nitrate and total nitrogen removal. In particular, the influence of various process and environmental parameters, particularly the residence time of the nitrate-containing water in the sludge or biomass bed, the oxygen concentration, the pH value, and the bed loading, on the nitrate and total nitrogen removal rates was analyzed. 1. Provision of biomass

[0075] The biomass pellets used to carry out the process according to the invention were obtained from a biological treatment stage for highly contaminated COD-containing wastewater. In the biological treatment stage, anaerobic, strongly reducing process conditions prevailed at a temperature of 36°C. Under these conditions, biomass pellets were formed which contained microorganisms involved in the nitrogen, methane, iron, and sulfur cycles and a carrier material containing lime, sulfur, iron, and nitrogen. The microorganisms formed a biofilm on the carrier material or grew on the carrier material. The pellets had an average particle size in the range of 5 to 8 mm, with the particle size of the pellets being determined using light microscopy. For use in the process according to the invention, the biomass pellets were separated from the COD-containing wastewater ortaken from the wastewater treatment stage and transferred to the reaction chamber for carrying out the process according to the invention. 2. Reactor technology

[0076] The process according to the invention was carried out in a single-stage CSTR ( continuously stirred tank reactor) or stirred tank reactor as a continuous process, whereby the reactor was fed with a bed of biomass based on the granulated pellets described above and nitrate-containing water. For the purposes of boundary layer renewal, the process was carried out with agitation of the biomass by slow stirring at less than two revolutions per minute. This caused the nitrate-containing water to flow through the reactor from the bottom in the inlet area upwards towards the outlet. On this basis, continuous boundary layer renewal and fluidization of the sludge or biomass bed formed by the biomass was made possible, thus ensuring the mass transfer required for nitrate degradation. At the same time, however, the purposefully adjusted stirring speed prevented mechanical destruction of the granulated pellets with the biomass.Further details regarding the reactor system used for the experiments described below can also be found in . Fig. 1A and 1B or the figure description above. 3. Process parameters and reaction conditions

[0077] Regarding the process parameters, the process according to the invention was carried out at a pH in the range of 7 to 7.5 and under at least substantially anoxic conditions, in particular a dissolved oxygen concentration in the nitrate-containing water in the range of 0 to 1 mg / l, based on the nitrate-containing water. The nitrate concentration in the nitrate-containing water in the influent was between 10 and 188 mg / l; the COD or COD concentration of the nitrate-containing water in the influent was between 5 and 10 mg / l. 4. Investigation of the total nitrogen degradation rate in various nitrate-containing waters

[0078] A general analysis of the nitrate removal performance of the process according to the invention, measured by the total nitrogen removal rate, was conducted using nitrate-containing waters from different sources. For this purpose, wastewater from drinking water treatment and raw water based on well water were used. Information on the analysis of the two waters used can be found in Tables 1 and 2 below: Tab. 1: Analysis of the well water used parameter Test procedures mg / l Phosphate, ortho (PO4-P) DIN EN ISO 15681 < 0,005 boron DIN 38405-D17 0,41 aluminum DIN 38406-E9 0,02 Ammonium DIN 38406-E5 0,03 Nitrate DIN 38405-D29 188,8 Nitrite DIN EN 26777 0,02 Sulfate DIN EN ISO 10304-1 462 Chloride DIN EN ISO 10304-1 115 Arsenic DIN EN ISO 11969 0,0041 Diaper DIN 38406-E6 < 0,01 Cadmium DIN EN ISO 5961 < 0,001 Calcium DIN EN ISO 7980 309 Chromium DIN EN 1233 < 0,01 Iron DIN 38406-E1 0,02 Potassium DIN 38406-E13 14,3 Copper DIN 38406-E7 < 0,01 Magnesium DIN EN ISO 7980 112 Manganese DIN 38406-E2 < 0,06 Nickel DIN 38406-E11 < 0,01 Zinc DIN 38406-E8 0,61 Tab. 2: Analytik des Abwassers aus der Trinkwasseraufbereitung Parameters Testing method mg / l Phosphate, ortho (PO4-P) DIN EN ISO 15681 0,010 TOC DIN EN 1484 10,2 Bor DIN 38405-D17 0,05 Aluminum DIN 38406-E9 0,04 Ammonium DIN 38406-E5 0,06 Nitrate DIN 38405-D29 100,0 Nitrite DIN EN 26777 0,03 Sulfate DIN EN ISO 10304-1 354 Chloride DIN EN ISO 10304-1 2217 Arsenic DIN EN ISO 11969 0,0029 Diaper DIN 38406-E6 < 0,01 Cadmium DIN EN ISO 5961 < 0,001 Calcium DIN EN ISO 7980 353 Chromium DIN EN 1233 < 0,01 Iron DIN 38406-E1 < 0,01 Potassium DIN 38406-E13 4,15 Copper DIN 38406-E7 < 0,01 Magnesium DIN EN ISO 7980 131 Manganese DIN 38406-E2 0,12 Sodium (W) DIN 38406-E14 30,2

[0079] In addition to the two aforementioned waters, the process according to the invention was also carried out with an artificially produced wastewater.

[0080] As part of the process used to investigate the nitrate degradation rate, the concentration of nitrate nitrogen or the nitrate content as well as the total nitrogen content in the nitrate-containing water were measured at the time of inflow. To analyze the nitrogen and nitrate elimination, the total nitrogen content in the treated water was also determined after completion of the inventive process, i.e., after completion of a maximum residence time of the nitrate-containing water in the biomass bed of 20 hours. From the measured values, the percentage total nitrogen degradation, i.e., the percentage reduction of the total nitrogen content compared to the values ​​for total nitrogen content or nitrate content measured in the inflow, was determined. The relevant results can be Fig. 2 From Fig. 2It can be seen that, using the process according to the invention, the total nitrogen content in the artificial wastewater could be reduced by approximately 25%, based on the initial value, to a total nitrogen content of 50 mg / l. In the well water, the total nitrogen content could be reduced by almost 70%, based on the initial value, to 10 mg / l. In the wastewater from drinking water treatment, the process according to the invention even achieved a total nitrogen reduction rate of over 90%, based on the initial value, to a total nitrogen content of 30 mg / l. 5. Weiterführender Untersuchung des Nitrate- und Stickstoffabbaus

[0081] In addition, the influences of pH, dissolved oxygen concentration, residence time of the nitrate-containing water in the sludge or biomass bed, and bed loading on the nitrate degradation rate were investigated. The results obtained in this regard are presented below. 5.1 Gesamtstickstoffbau gemessen an der Aufenthaltszeit

[0082] In a further series of experiments, the development of the total nitrogen degradation rate during the residence time of the nitrate-containing water in the sludge or biomass bed was investigated. The nitrate-containing wastewater from drinking water treatment used for this purpose had a total nitrogen content of 30 mg / l in the inlet, i.e., at the beginning of the process according to the invention. The process was carried out over a maximum duration of 22 hours, or with a residence time of the nitrate-containing water in the reactor of a maximum of 22 hours. The total nitrogen degradation rate over the entire residence time was determined by regularly determining the total nitrogen content in the nitrate-containing water. The results obtained in this regard are presented in Fig. 3 shown. From Figure 3It can be seen that the total nitrogen degradation rate increases sharply after a residence time of 8 hours, and saturation of the degradation occurs after approximately 18 to 22 hours. In light of these results, a residence time of the nitrate-containing water in the reactor or biomass bed in the range of 8 to 22 hours appears particularly suitable for the process according to the invention. 5.2 Residence time, pH value and dissolved oxygen concentration

[0083] Furthermore, the degradation rate of total and nitrate nitrogen was investigated as a function of residence time, pH, and dissolved oxygen concentrations in the nitrate-containing water. The process according to the invention was carried out as a continuous process. Fig. 4A First, the respective residence times (Δ t,SB) of the nitrate-containing water in the sludge or biomass bed was visualized. The residence times ranged from 7 to 12.5 hours. Furthermore, the pH value and dissolved oxygen concentration in the nitrate-containing water were measured during the nitrate elimination process. The respective measured values ​​are Fig. 4B can be found. From Fig. 4B It can be seen that the process was carried out with dissolved oxygen concentrations between 0 and 0.3 mg / l, ie under essentially anoxic conditions, and at pH values ​​between 7.1 and 7.3. In Fig. 4CFinally, the nitrate removal rates (NO 3 removal) and total nitrogen removal rates (Tn B removal) achieved under the aforementioned conditions, i.e., residence time, dissolved oxygen concentration, and pH, are presented. Over the entire process duration, total nitrogen removal rates between approximately 20 and 65% were measured, and nitrate nitrogen removal rates in the range of 30 to 80% were also measured. Overall, therefore, with the process parameters described above, a significant reduction in the total and nitrate nitrogen content in the nitrate-containing water can be measured and recorded. 5.3 Length of stay and bed load

[0084] Finally, the nitrate degradation rate by the process according to the invention was specifically investigated as a function of the residence time of the nitrate-containing water in the sludge or biomass bed and the bed loading used. The nitrate-containing waters used for this purpose had a nitrate concentration of approximately 100 mg / l in the influent.

[0085] Fig. 5A shows the results obtained in relation to the residence times. The nitrate degradation rate was investigated for residence times between 6.5 and 12 hours. Particularly good degradation rates were obtained when the residence time was between 8 and 12 hours. With residence times of the nitrate-containing water in the range of 8 and 12 hours, the nitrate nitrogen concentration could even be reduced below the limit of 50 mg / l specified in the Drinking Water Ordinance.

[0086] In Fig. 5B The nitrate degradation rates are shown as a function of the bed load used. The influence of the bed load was investigated using two different waters. Overall, Fig. 5BIt is evident that the nitrate degradation rate generally decreases with increasing bed load. With a bed load between 10 and 80 gN / m³ / d, nitrate degradation rates between 30 and 100% were achieved. With a maximum bed load of 60 gN / m³ / d, the nitrate concentration in the nitrate-containing water could even be reduced to values ​​below the permitted limit of 50 mg / l for drinking water. 6. Conclusion

[0087] Based on the results described above, it is clear that the process according to the invention can achieve significant nitrate elimination in nitrate-containing water. The process according to the invention allows a safe reduction of the nitrate nitrogen content to values ​​below the permissible limit of 50 mg / l for drinking water. Furthermore, the nitrate and total nitrogen removal rate can be improved by targeted adjustment of bed loading and residence time, as well as pH and dissolved oxygen concentration.

[0088] Based on the examples described above, it is evident that particularly good results with regard to nitrate and total nitrogen removal are achieved with the process parameters listed in Table 3 below. With the following process parameters, nitrate removal rates of over 50%, based on the original nitrate content of the nitrate-containing water, can be achieved. With an original nitrate content of 100 mg / l in the nitrate-containing water, water can thus be provided that meets the requirements of the Drinking Water Ordinance regarding nitrate content. Tab. 3: Preferred process parameters according to the invention parameter Unit min. max. PH value 7 7,5 Dissolved oxygen concentration mg / l 0 1 Residence time h 8 22 Bed load gN / m 3 < / d 30 65 Nitrate concentration in the inlet mg / l 10 100 COD concentration in the inlet mg / l 5 10 List of reference symbols:

[0089] 1Reactor system 2Reactor tank 3Agitator shaft 4Inlet 5Outlet 6Overflow 7Receiver / feed vessel 8Valve 9Measuring devices 10Motor / drive 11Biomass 12Nitrate-containing water 13Rotation stirrer 14Flow 15Pumps

Claims

1. Process for the biological reduction of the nitrate nitrogen concentration in nitrate-containing water with microbial nitrate elimination, wherein the nitrate elimination is carried out lithotrophically and with the use of biomass or colonization of biomass or both, wherein the nitrate-containing water is passed through a reaction chamber and wherein the biomass contains microorganisms, involved in the nitrogen cycle, methane cycle, iron cycle and sulphur cycle, in particular bacteria or archaea or both, wherein activated sludge obtained from a heterotrophic, anaerobic activated sludge process for the treatment of wastewater containing COD is used as biomass, wherein the nitrate-containing water has a nitrate concentration in the range from 5 to 500 mg / l and a chemical oxygen demand COD [mg O2 / l] in the range from 0 to 50 mg / l, in each case based on the nitrate-containing water at the time of feeding into the reaction chamber, wherein the process is carried out under anoxic conditions, wherein the process is carried out under continuous boundary layer renewal on the surface of the biomass wherein the process is carried out as a one-step process and the process is carried out at a pH value in the range from 6 to 8.

2. The process according to claim 1, wherein the process is carried out without supplying organic carbon sources.

3. The process according to claim 1 or 2, wherein raw water and / or waste water, in particular raw water, is used as nitrate-containing water and / or wherein the nitrate-containing water has a chemical oxygen demand COD [mg O2 / l] in the range from 0 to 25 mg / l, further preferably 0 to 10 mg / l, based on the nitrate-containing water at the time of feeding into the reaction chamber.

4. The process according to one of the preceding claims, wherein the nitrate-containing water has a biological oxygen demand BOD5 in the range from 0 to 75 mg / l, in particular at most 50 mg / l, preferably at most 40 mg / l, further preferably at most 30 mg / l, particularly preferably at most 20 mg / l, based on the nitrate-containing water at the time of feeding into the reaction chamber.

5. The process according to any one of the preceding claims, wherein the nitrate-containing water has a nitrate concentration in the range from 8 to 250 mg / l, most preferably 10 to 100 mg / l, based on the nitrate-containing water at the time of feeding into the reaction chamber.

6. The process according to any one of the preceding claims, wherein the biomass forms a biofilm on a carrier material, in particular wherein the carrier material contains (i) inorganic and / or organic, preferably inorganic salts, in particular carbonates, particularly preferably calcium carbonate (lime); (ii) metals and / or transition metals, in particular iron; and / or (iii) non-metals, in particular sulphur and / or nitrogen.

7. The process according to claim 6, wherein biomass is used in the form of granules and / or pellets, in particular wherein the granules and / or pellets have an average particle size, in particular an average particle diameter, in the range from 0.01 to 150 mm, in particular 0.05 to 100 mm, preferably 0.1 to 50 mm, preferably 1 to 25 mm, more preferably 2 to 20 mm, further preferably 3 to 15 mm, even more preferably 5 to 10 mm.

8. The process according to any one of the preceding claims, wherein the biomass, preferably the biomass in the form of granules and / or pellets, is fluidized and / or dispersed in the nitrate-containing water.

9. The process according to any one of the preceding claims, wherein the process and / or the nitrate elimination is carried out with a bed load [amount of nitrogen per volume of biomass per unit time] in the range from 0.5 to 1,000 gN / m3 / d, in particular 1 to 500 gN / m3 / d, preferably 5 to 250 gN / m3 / d, preferably 10 to 100 gN / m3 / d, particularly preferably 30 to 65 gN / m3 / d.

10. The process according to any one of the preceding claims, wherein the boundary layer renewal is carried out by generating a flow in the nitrate-containing water and / or the biomass.

11. The process according to claim 10, wherein the boundary layer renewal is carried out by stirring, in particular wherein stirring speeds in the range from 0.1 to 50 revolutions per minute, in particular 0.5 to 25 revolutions per minute, preferably 0.7 to 20 revolutions per minute, preferably 1 to 10 revolutions per minute, particularly preferably 1.2 to 5 revolutions per minute, even more preferably 1.5 to 2 revolutions per minute, are used.

12. The process according to any one of the preceding claims, wherein the process and / or the nitrate elimination is carried out at a pH in the range from 7 to 7.5.

13. The process according to any one of the preceding claims, wherein the process and / or the nitrate elimination is carried out with dwell time of the nitrate-containing water in the reaction chamber in the range from 0.5 to 100 hours, in particular from 1 to 80 hours, preferably from 2 to 50 hours, preferably from 5 to 25 hours, particularly preferably from 8 to 22 hours.

14. The process according to any one of the preceding claims, wherein the method is followed by post-aeration, in particular wherein the post-aeration is carried out in the same or a separate reaction chamber, preferably a separate reaction chamber.

15. The process according to any one of the preceding claims, wherein the process is followed by secondary clarification and / or precipitation and / or flocculation, in particular wherein the secondary clarification and / or precipitation and / or flocculation is carried out in the same or a separate reaction chamber, preferably a separate reaction chamber.